Conventionally, a mobile telephone capable of performing a group communication among a plurality of users, forming a group of a plurality of users, is well-known. Particularly in recent years, there is an attempt to perform the group communication by voice, via a packet exchange network, using VoIP (Voice Over Internet Protocol). An example of the group communications is called PTT (Push To Talk). A radio telephone and a PTT system having a PTT function are disclosed in Patent Document 1.
Here, PTT is described briefly in the following.
In the PTT, a server is provided on a network, and the server performs communication control among users, along with managing a group formed by a plurality of users.
To describe specifically, firstly, a user who wants to be a speaker first chooses one or more communication partners, and transmits a communication request to the communication partners via the server. When the communication partners respond to the communication request, the responding communication partners become listeners. Then a group of a speaker and listeners is formed and the group communication begins. When this group communication begins, information indicating whether the number of listeners is one or plural is transmitted from the server to respective mobile telephones of the speaker and the listeners. Along with the transmission of the information, if the respective mobile telephones have display unit such as liquid crystal display (LCD) device and the like, displays as shown in FIGS. 15A and 15B, for example, are displayed thereon. That is, when the number of listeners other than the speaker is one, an icon as shown in FIG. 15A is displayed and when the number of listeners other than the speaker is plural, an iconic display as shown in FIG. 15B is displayed. Thus, when the PPT communication begins, only the speaker having a floor (a right to speak) is permitted to speak. So, if a listener wishes to speak as a speaker, the listener has to make a new request to the server for the acquisition of the floor, after the speaker finishes speaking and releases the floor. When the server having received the request grants permission, the listener acquires the floor and becomes a new speaker, being permitted to speak.
Thus, a plurality of mobile telephones take turns acquiring the floor under the management of the server, which allows alternation or rotation of a speaker and listeners, realizing the group communication.
Note that, in the present description, communication where there is only one listener is called “one-to-one” communication and communication where there are a plurality of listeners is called “one-to-many” communication.    Patent Document 1: Laid-Open Patent Publication No. 2002-536928